This application relates to copending application Ser. No. 554,174 filed Nov. 22, 1983 now abandoned, entitled "Process for Dry Deinking of Secondary Fiber Sources".
The commercial production of various types of paper requires the use of recycled paper as a source of papermaking fibers due to the expense of virgin fibers. Prior to using such secondary fiber sources for making a commercial product, it is necessary to treat the fiber source to remove unwanted chemical constituents which adversely affect the quality of the final paper product. The most notable contaminants to be removed are inks or dyes which adversely affect the color and brightness of secondary fibers used as a feedstock. Ink deposits on paper are extremely thin and roughly have a thickness of only about 0.0001 inch. Chemically, the inks are generally a mixture of pigment or organic dye, binder, and solvent. Some inks also contain metallic driers, plasticizers, and waxes to impart desired properties. Hence, their chemical make-up can be very complex. However, inks are not to be equated with other additives or contaminants such as varnishes, sizes, and plasticizers, which are chemically and physically of a different nature as those skilled in the art of deinking will appreciate.
The prior art has addressed secondary fiber clean-up generally by subjecting secondary fiber sources to a variety of treatments. The most common form of treatment is chemical wet deinking. However, wet deinking processes can be expensive and produce large quantities of sludge, which creates a disposal problem. In addition, there are certain types of papers which cannot be successfully deinked at all by conventional wet methods because they are chemically unreactive with the deinking agents.
Other treatments of secondary fibers have been directed toward separating other contaminants besides inks from the secondary fibers, such as plastic coatings and miscellaneous particulates. For example, French Pat. No. 1295608 (1961) teaches recovery of waste paper coated with synthetic materials or plastic films by wetting the waste paper and subjecting the slurry to attrition in a beating device. The hydrophobic plastic particles can be separated from the hydrophylic fibrous material, which has been disintegrated by the attrition mill into particles (fibers) which are smaller than the plastic particles. British Pat. No. 940,250 (1963) teaches a method for recovering fibrous materials from waste paper products which have been coated with synthetic resins in the form of a rigid film. The waste material is exposed to vigorous mechanical treatment in the presence of less than 70 weight percent water to fiberize the material, while leaving the synthetic resin film in relatively large pieces. British Pat. No. 1228276 (1971) teaches a method for recovering fibrous material from plastic coated or plastic-containing wastepaper. The wastepaper is fiberized in water whereby the plastic separates from the fibers in small particles. The plastic particles are then separated from the fibers. A Russian article entitled "Dry Comminution of Waste Paper:, M. V. Vanchakov, V. N. Erokhin, M. N. Anurov (Jan. 14, 1981) teaches dry grinding of wastepaper in a hammermill as a pretreatment prior to a hydropulper to separate large contaminants such as fasteners, cloth, polyethylene film, and others. The ground material was passed through separator screens having 4 mm. and 8 mm. diameter holes and the fractions passing through the screens were defiberized in a hydropulper. However, as suggested previously, none of these methods are directed to deinking. All are concerned with removal of plastic films and coatings, which separate out as relatively large pieces. Also, except for the Russian article, all of these methods use water and accordingly are not suggestive of a dry process. On the other hand, the Russian article does not suggest deinking, but rather is directed toward removal of large contaminants rather than fines.
Still other prior methods of treating waste papers use different approaches. For example, U.S. Pat. No. 3,736,221 (1973) to Evers et al teaches a method for making shaped bodies from wastepaper by fiberizing the wastepaper in a hammermill, coating the fibers with an aqueous binder, compressed under pressure, and baked. No effort is made to remove the ink from the wastepaper. U.S. Pat. No. 4,124,168 (1978) to Bialski et al teaches a method for recovering different types of wastepaper from a mixed source by fragmenting the source materials and separating the various components by their fragmentability. This method only serves to classify various types of wastepaper present in a mixed sample and does not attempt to remove the ink from the wastepaper. German Pat. No. 1097802 (1961) teaches a method for reclaiming wastepaper by tearing the paper and cleaning it, crimping and rolling the torn paper in a practically dry state, and defibering in the dry state, optionally in the presence of dry steam. This method seeks to overcome difficulties in fiberizing wastepapers coated with hydrophobic materials which do not respond well to aqueous methods. There is no teaching, however, that inks can be removed by such a dry treatment.
The previously mentioned copending application Ser. No. 554,174 also published in Belgian Pat. No. 898,500, issued Jan. 16, 1984, describes an invention which has overcome the disadvantages of the abovesaid prior deinking methods. The process involves fiberizing an ink-containing secondary fiber source, substantially dry, wherein individual fibers and ink-containing fines are produced. The fibers and fines are then separated by any suitable means, such as by depositing the material on a moving wire and drawing the fines down through the wire with a vacuum on the underside of the wire. However, it has been found that the initial deposition of the fibrous material onto the screen may not necessarily remove all of the fines present in the fibrous material, particularly if the resulting layer of fibers is too thick. Therefore, improvements to the separation step can be useful.